The present invention relates to a refrigerating system and, more particularly, to a hermetic motor-compressor for a refrigerating system.
The refrigerating system has a closed refrigerant circuit comprising a refrigerant compressor, condenser, pressure reducer and an evaporator which are connected in series by means of pipes.
The compressed refrigerant gas discharged from the refrigerant compressor is cooled and liquefied in the condenser, and the liquefied refrigerant flows into the evaporator after a pressure reduction by the pressure reducer. The refrigerant of reduced pressure then absorbs heat from a fluid to be cooled, while passing through the evaporator, thereby to be evaporated and then returned to the refrigerant compressor completing one refrigerating cycle. The fluid to be cooled is cooled by the heat absorption performed in the evaporator, and is used for various purposes.
Hermetic motor-compressors now find widespread use as the refrigerant compressor. This type of compressor has an electric motor component and a compressor component disposed in a closed container and operatively connected to each other. The hermetic motor-compressor, however, has the following problems.
Since the compressor component is confined in the closed container and thermally insulated from the ambient air by the closed container, the compressor component reaches such a high temperature that it undesirably heat the ambient refrigerant gas within the closed container. In consequence, the refrigerant gas of a low temperature, which has been returned from the evaporator to the hermetic motor-compressor and uniformly dispersed in the closed container, is heated and the temperature of the refrigerant gas sucked into the compressor component through a suction pipe opening in the closed container is raised. As a result, the specific weight of the refrigerant gas is increased to decrease the flow rate by weight of the refrigerant gas, resulting in a reduced volumetric efficiency of the compressor.
In the refrigerating system, the reduction of the volumetric efficiency causes a drop of the refrigerating power per unit input.
The refrigerant gas dispersed in the closed container flows, particularly when the return pipe is connected to a point near the top of the closed container, downwardly along the outer walls of the electric motor component and the compressor component and, therefore, is heated by the hot outer wall of the compressor component. The reaction of the downward flow of refrigerant gas forcibly drives the heated refrigerant gas in the container upward and inconveniently scatters the lubricating oil from an oil reservoir defined at the bottom of the closed container. The lubricating oil scattered upward is sucked together with the refrigerant gas into the compressor component through a suction pipe standing up from the cylinder head to cause not only the reduction of the volumetric efficiency but also an oil hammering.
U.S. Pat. No. 3,008,628 to K. M. Gerteis et al discloses a hermetic motor-compressor which is arranged such that the lubricating oil in the crank chamber is discharged into an oil reservoir by using blow-by gas coming from the cylinder. In the motor-compressor disclosed in the Gerteis et al patent, the electric motor component and the compressor component are separated from each other, in a vertical direction, by a partition wall. The motor and compressor assembly, having a crankshaft and motor shaft integral therewith, is housed within a closed container through a flange provided at the top of a cylindrical member surrounding the compressor component, and an oil tank or reservoir is formed around the cylindrical member. The refrigerant gas returned into the closed container flows through a passage formed around the outer periphery of the motor component and through a gap between the stator and rotor of the motor component to effectively cool the motor component, before it is sucked into the cylinder through a space beneath the motor component and an opening formed in the partition plate. Thus, the refrigerant gas itself is heated, although the motor component is cooled effectively.
U.S. Pat. No. 3,486,687 to R. W. Ayling discloses a hermetic motor-compressor which is arranged such that liquid refrigerant flowing into the closed container is evaporated by the heat delivered by the hot compressor component to prevent the dilution of the oil by the liquid refrigerant. In the motor-compressor disclosed in the Ayling patent, the motor and compressor components are housed within a closed container with the motor component disposed above the compressor component. The compressor component is encased by an inner casing which is in contact with the parts adapted to be heated to a high temperature, e.g. head cover, discharge muffler and the like, thereby to constitute a heat exchanger for the hot compressor component. The liquid refrigerant returned into the closed container through a suction port formed in the latter, therefore, is made to drop into the inner casing and is evaporated because of heat-exchange thereof with the hot parts. The refrigerant gas is heated by the inner casing and the hot compressor component to a high temperature before it is sucked into the cylinder.